In the formulation of drug compositions, it is important for the drug substance to be in a form in which it can be conveniently handled and processed. This is of importance, not only from the point of view of obtaining a commercially viable manufacturing process, but also from the point of view of subsequent manufacture of pharmaceutical formulations comprising the active compound.
Further, in the manufacture of drug compositions, it is important that a reliable, reproducible and constant plasma concentration profile of drug is provided following administration to a patient.
Chemical stability, solid state stability, and “shelf life” of the active ingredients are also very important factors. The drug substance, and compositions containing it, should preferably be capable of being effectively stored over appreciable periods of time, without exhibiting a significant change in the active component's physico-chemical characteristics (e.g. its chemical composition, density, hygroscopicity and solubility).
Moreover, it is also important to be able to provide drug in a form which is as chemically pure as possible.
Amorphous materials may present significant problems in this regard. For example, such materials are typically difficult to handle and to formulate, provide for unreliable solubility, and are often found to be unstable and chemically impure.
The skilled person will appreciate that, if a drug can be readily obtained in a stable crystalline form, the above problems may be solved.
Thus, in the manufacture of commercially viable, and pharmaceutically acceptable, drug compositions, such as modified-release compositions, it is important, wherever possible, to provide drug in a substantially crystalline, and stable, form.
It is to be noted, however, that this goal is not always achievable. Indeed, typically, it is not possible to predict, from molecular structure alone, what the crystallisation behaviour of a compound will be. This can usually only be determined empirically.
2. Prior Art
International patent application WO 01/28992 discloses a number of oxabispidine compounds, including: